Conventionally, the duct used for air conditioning or venting equipment (FIG. 12) is formed in a cylinder having a rectangular section by connecting two pairs of plate members 1, 2 using a joint structure of what is called "the button punch snap seam" as shown in FIG. 10 or what is called "the Pittsburgh seam" as shown in FIG. 11.
The former joint structure is such that the forward end portion of a plate member (first plate member) 1 constituting one joint portion is bent substantially at right angle, an end 1A of the bent portion is fitted into a U-shaped portion 2A at the end portion of a plate member (second plate member) 2 constituting the another joint portion thereby to form a joint. In this case, what is called "the return stops" 1a are formed at the end 1A on the first plate member 1 and adapted to engage an engaging portion 2b formed at the end of the second plate member 2. The forward end portion of the first plate member 1, once fitted as shown in FIG. 10b, therefore, would never come off. Therefore, the jointing work is very simple and requires no trouble other than fitting.
For the latter "Pittsburgh seam", on the other hand, as shown in FIG. 11, a bent end A1 at the forward end portion of a plate member (first plate member) 1 constituting one of the joint portion is fitted into a U-shaped portion 2A at an end portion of a plate member (second plate member) 2 constituting the other joint portion. Then, a protruded end portion 2c of the second plate member 2 is bent along the side 1b of the first plate member 1, as shown in FIG. 11b thereby to form a joint. In this case, the end 1A of the first plate member 1 is fixed (pressed) from above by the protruded end portion 2c of the second plate member 2. Once the joint structure is complete, therefore, the first plate member 1 would never come off. In addition, the double fitted structure of the joint including the first plate member 1 and the second plate member 2 has a considerably improved strength and a high hermeticity.
Consequently, a duct joint requiring hermeticity employs the "Pittsburgh seam".
In current practice, the work of forming the joint of the button punch snap seam and the Pittsburgh seam described above, i.e., the duct assembly work, is performed by the worker hitting a corner 4 of the plate member 1 or the neighborhood thereof to fit it into the second plate member 2. Actually, however, the joint is made of plates (steel-plate or the like) as thin as 0.3 to 1.2 mm. Strictly speaking, therefore, the plate member 1 or 2 is not sufficiently linear to allow the bending work for easily fitting the plate members along the longitudinal direction of the duct. As a result, the fitting work requires a considerable magnitude of force and a multiplicity of hits by the hammer. The fitting work (assembly work), therefore, must be performed by a very strong person. In addition, the hitting sound of the hammer is so harsh to the ears as to possibly cause the worker a hearing problem. In the absence of suitable soundproof equipment, therefore, the complaints against the noise would rush in from the neighboring residents. A similar problem is posed by the work of bending the protruded end portion 2c of the second plate member 2 described above.
Further, the time consuming manual work of said assembly is low in efficiency and the duct is therefore expensive to fabricate.
In addition, the manual work makes it impossible to assemble the duct (fit the joint) at the construction site where the working time is limited. Unavoidably, therefore, the duct is presently assembled and stored in the factory, and transported the site using a truck and crane in accordance with the progress of the field work. Also, the delivery of an assembled duct in a truck encounters the problem of a bulkiness for the weight, leading to a very low transportation efficiency. What is more, the duct cannot be securely bound by rope or the like as it would be deformed. The result is a high risk of dropping the assembled duct in transit.
Furthermore, when hoisting the duct to the desired building floor by crane at the site, the small weight and the bulkiness exposes the hoisting work to the direct effect of the wind. It is therefore very difficult to deliver the duct into desired position by crane.
Another very troublesome problem posed by the bulkiness for the duct suppliers is that temporary storage of the duct where it is to be mounted interferes with the water or electricity work conducted concurrently. Also, the bulkiness is a factor which makes it impossible to store a large amount of standardized ducts in the factory. Even in the custom production, storage of completed ducts requires a large space.
Also, the conventional duct hanger, as shown in FIG. 25, is composed of an angle steel member 50 cut to the width of a duct 10 and having each end thereof formed with a hole 50a through which to apply a rod member 30.
In such a case, the duct work for an ordinary building requiring ducts of a variety of widths makes it necessary to prepare the angle steel member meeting the varying width of the duct. Also, this hanger, as shown in FIG. 24, must always be hanged by a pair of steel rod members for structural reasons. As a result, the place where the hanger can be installed is limited by the building structure and equipment. Another inconvenience is the fact that the duct is hanged at unnecessarily short pitches on the inner periphery side of the corners thereof. In addition, the angle steel member, when hanged by the ends thereof with steel rods, is liable to undesirable rotate about the steel rod members.
Another disadvantage of the conventional duct hanger system is that since the duct is only placed on the angle steel member , an air flow, if any, in the duct is a frequent cause of duct vibrations and noises in cooperation with the angle steel member.
The present invention has been developed in view of the above-mentioned situation, and the object of the invention is to provide a duct joint structure, an assembly tool, a duct assembly method and a hanger most suitable for the duct with the joint structure, which is not bulky and therefore convenient for storage or transportation, can be fitted quickly, and can be assembled easily even by a worker of less than average strength with a minimum of assembly noises.